Got a small leak in the hot water tank which is in the bedroom upstairs.It must have been leaking for sometime as there is a white crispy build up round the big nut.The leak is on the side of the tank where a pipe comes out half way up it on a T branch. One part of the pipe is from the radiator pump and the other part turns 90% upwards and stops at a length of 8 inches. This has a cap/screw in it I think I see threads there.